1. Field of the Invention
The present invention relates to an optical switch used in changing the path of an optical signal, and more particularly, to an optical switch configured such that even if a vibration or oscillation should be transmitted to the optical switch, the operating or performance characteristic of the optical switch is not deteriorated.
2. Description of the Related Art
For the purpose of changing the path of an optical signal propagating through an optical waveguide such as an optical fiber, various types of optical switches have been heretofore used. An example of the prior art optical switch will be described with reference to FIGS. 1 to 4.
FIG. 1 is a plan view illustrating a construction of the prior art optical switch, and FIG. 2 is a sectional view taken along the line 2xe2x80x942 in FIG. 1 and looking in the direction indicated by the arrows. The illustrated switch SW comprises: a movable electrode supporting frame 10 of a generally square in plan; a stationary electrode substrate 8 of a generally square in plan that closes the interior space of the movable electrode supporting frame 10; a movable electrode plate 2 of a generally square in plan that is disposed substantially in parallel with the stationary electrode substrate 8 with a space or gap between them generally in the center of the top surface of the stationary electrode substrate 8, that is, generally in the center of the movable electrode supporting frame 10; four elastic and flexible beams 21 for supporting the movable electrode plate 2 for up and down or vertical motion, each beam having a plurality of meanders or sharply turning portions, one end thereof being fixed to corresponding one of the four sides of the movable electrode plate 2 generally in the center of the side and the other end thereof being fixed to corresponding one of the four sides of the movable electrode supporting frame 10 generally in the center of the side; and a mirror 3 mounted on the center of the top surface of the movable electrode plate 2 along one diagonal line thereof.
Generally in the center of each of the four sides of the movable electrode supporting frame 10 is formed a post-like connecting portion 211 protruding upwardly and formed integrally with the supporting frame 10. The other end of each beam 21 is fixed to corresponding one of these connecting portions 211.
The movable electrode supporting frame 10 is configured by boring a generally square opening 12 through a silicon substrate of a generally square in plan, the opening 12 being bored concentrically with the silicon substrate. In case of boring the opening 12, as will be easily understood from FIG. 2, it is preferable that the opening 12 is perforated such that the wall surface of the opening 12 has a taper or slant so that the bore (size) of the opening 12 is gradually increased toward the lower portion thereof, and also it is preferable that the outer wall surface of the generally square stationary electrode substrate 8 is formed so as to have the same taper or slant as that of the opening 12. It is needless to say that the thickness of the stationary electrode substrate 8 is set to the same value as that of the silicon substrate (the depth of the opening 12). By such arrangements, it is possible to fit and fix the stationary electrode substrate 8 in the opening 12 of the movable electrode supporting frame 10 in the state that the stationary electrode substrate 8 is electrically insulated from the supporting frame 10 by inserting the stationary electrode substrate 8 into the opening 12 from the bottom side thereof. As a result, the movable electrode supporting frame 10 and the stationary electrode substrate 8 are integrally coupled and become one plate-like body of a generally square.
Further, as one method of electrically insulating the junction between the movable electrode plate 2 and the stationary electrode substrate 8, it is considered that the stationary electrode substrate 8 will be formed out of an n-type silicon semiconductor, for example, and the movable electrode plate 2 will be formed out of a p-type poly-silicon semiconductor, thereby to form the p-n junction therebetween, and a reverse bias voltage or current will be applied to the p-n junction, which results in the electrical insulation between the movable electrode plate 2 and the stationary electrode substrate 8. It goes without saying that the junction between the movable electrode plate 2 and the stationary electrode substrate 8 may also be electrically insulated by use of other methods.
In addition, as will be easily understood from the sectional view of FIG. 2, the four beams 21, the movable electrode plate 2, the four connecting portions 211, and the movable electrode supporting frame 10 are usually formed integrally with one another. That is, in case of forming the four connecting portions 211 on the movable electrode supporting frame 10 using a semiconductor integrated circuit manufacturing technique, the movable electrode plate 2 and the four beams 21 are formed at the same time. Consequently, the four beams 21, the movable electrode plate 2, the four connecting portions 211 and the movable electrode supporting frame 10 are formed integrally with one another. Since such manufacturing method for the optical switch SW is well known, the explanation thereof will be omitted here.
Next, the operation of the optical switch SW constructed as discussed above will be described with reference to FIGS. 3 and 4.
FIG. 3 is a plan view for explaining the above-constructed optical switch SW in practical use, wherein the optical switch SW is shown in plan view similar to FIG. 1. An input side optical waveguide, namely an optical fiber 4 in this example, for inputting an optical signal L into the optical switch SW is positioned at the left side of the optical switch SW in the drawing. An output side optical waveguide, namely an optical fiber 5 in this example, for transmitting the optical signal L supplied from the optical switch SW is aligned with the input side optical fiber 4 along a straight line passing through the mirror 3 at an angle of about 45xc2x0 with the surface of the mirror 3, and another output side optical waveguide, namely an optical fiber 6 in this example, for transmitting the optical signal L supplied from the optical switch SW is disposed on a straight line passing through the mirror 3 and orthogonal to the aforesaid straight line.
FIG. 4 is a diagrammatical sectional view illustrating the manner that the optical switch SW shown in FIG. 3 is accommodated in a package 9 which is shown by only a pedestal 91 for putting the optical switch on the top thereof and fixing it thereto, and the peripheral or neighboring portion of the pedestal 91. Further, the optical switch SW is shown by a sectional view taken along the line 4xe2x80x944 in FIG. 3 and looking in the direction indicated by the arrows. The input side optical fiber 4 and the output side optical fiber 5 are not sectioned.
As described above, since the mirror 3 is placed on the central portion of the movable electrode plate 2 along a diagonal line thereof, the optical signal L that is outputted from the output end of the input side optical fiber 4 and goes right on in a space is incident on the mirror 3 at an angle of about 45xc2x0 with the surface of the mirror 3. As a result, the optical signal L is reflected by the mirror 3 in the direction of forming an angle of 90xc2x0 (forming a right angle) with the incident light (the optical signal L is outputted from the mirror 3 at an angle of about 45xc2x0 which is the same as the incident angle), and is transmitted to the input end of the output side optical fiber 6. In the specification, the transmission state of the optical signal L in which the optical signal L outputted from the input side optical fiber 4 is reflected by the mirror 3 and transmitted to the output side optical fiber 6 is defined as the steady state.
In the above steady state, in case of applying a predetermined voltage between the movable electrode plate 2 and the stationary electrode substrate 8 to generate an electrostatic force between the both electrodes in such manner that they are attracted each other, the beams 21 are elastic and flexible and the stationary electrode substrate 8 is immovable, and hence the movable electrode plate 2 is driven downwardly toward the stationary electrode substrate 8. Accordingly, if a voltage applied between the movable electrode plate 2 and the stationary electrode substrate 8 is controlled to displace or drive the movable electrode plate 2 downwardly so that the mirror 3 fixed to the top surface of the movable electrode plate 2 is displaced or driven downwardly to a position where the mirror 3 is out of the optical path on which any optical signal outputted from the input side optical fiber 4 goes right on, the optical signal L outputted from the input side optical fiber 4 will go right on without being reflected by the mirror 3 and be transmitted to the output side optical fiber 5. Thus, the optical signal L incident on the optical switch SW can be switched to any one of the two output side optical fibers 5 or 6 for transmission of it therethrough. In other words, the above-configured optical switch SW is capable of switching in space the path of an optical signal propagating through an optical waveguide or optical transmission line (path) without any intervention of a solid state optical waveguide.
However, as shown in FIG. 4, in case the optical switch SW is accommodated in the package 9, the bottom surface of the stationary electrode substrate 8 of the optical switch SW is fixed directly to the pedestal 91 of a generally square in plan formed on the package 9 by an appropriate adhesive agent, for example. For this reason, if a mechanical vibration or oscillation is transmitted to the package 9 from the outside thereof, the vibration is transmitted to the movable electrode plate 2 through the pedestal 91 of the package 9, the stationary electrode substrate 8 of the optical switch SW, the movable electrode supporting frame 10, the connecting portions 211, and the beams 21 in order of the description. As a result, the movable electrode plate 2 vibrates, and hence the mirror 3 secured to the movable electrode plate 2 vibrates, which results in a drawback that the operating characteristic of the optical switch SW is deteriorated.
It is an object of the present invention to provide an optical switch that the operating characteristic thereof is not influenced for bad by a vibration or oscillation.
It is another object of the present invention to provide an optical switch that any vibration or oscillation transmitted to a package is decreased by damping effects of a diaphragm and a space area thereby to prevent the vibration or oscillation from being transmitted to a movable electrode of the optical switch.
In order to accomplish the foregoing objects, in one aspect of the present invention, there is provided an optical switch which comprises: a stationary electrode; a movable electrode opposed to the stationary electrode with a predetermined space therebetween; and a mirror mounted to said movable electrode, wherein the movable electrode and the mirror are moved together by applying a voltage between the stationary electrode and the movable electrode thereby to switch the path of an incident optical signal to the optical switch, and being characterized in that a buffer member provided with a diaphragm is attached to the bottom of the stationary electrode.
In a preferred embodiment, the aforesaid buffer member comprises: a diaphragm of a predetermined thickness; a peripheral wall formed on and integrally with the periphery of the diaphragm for supporting the diaphragm and including a first frame-like portion protruding upwardly from the top surface of the diaphragm and a second frame-like portion protruding downwardly from the bottom surface of the diaphragm; at least one ventilating cutout formed in the first frame-like portion of the peripheral wall on the top surface side of the diaphragm; and a pedestal mount portion formed on and integrally with substantially the central portion of the bottom surface of the diaphragm and protruding downwardly.
In addition, the first frame-like portion of the peripheral wall of the buffer member on the top surface side of the diaphragm is joined with the bottom surface of the stationary electrode to form a space area communicating with the outside atmosphere through only the cutout between the top surface of the diaphragm and the bottom surface of the stationary electrode, and an external vibration or oscillation is substantially prevented from being transmitted to the movable electrode by the damping effects of the diaphragm and the space area.
In a specific example, the height of the first frame-like portion of the peripheral wall of the buffer member on the top surface side of the diaphragm is about 5 xcexcm, and the space area having its thickness of about 5 xcexcm is formed between the top surface of the diaphragm and the bottom surface of the stationary electrode.
In addition, the diaphragm of the buffer member is formed from a generally square or rectangular silicon substrate, and the peripheral wall of a generally square or rectangle formed on and integrally with the periphery of the diaphragm and the pedestal mount portion formed on and integrally with substantially the central portion of the bottom surface of the diaphragm are also formed from said silicon substrate, and the cutout reaching the top surface of the diaphragm is formed on the generally square or rectangular first frame-like portion of the peripheral wall on the top surface side of the diaphragm at opposed positions thereof.
With the construction as described above, between the bottom of the stationary electrode and the top surface of the diaphragm of the buffer member is formed a space area communicating with the outer atmosphere through only the cutout. Since the space area acts like an air cushion, its damping effect to a vibration or oscillation is remarkable as well as the diaphragm. Consequently, even if an external mechanical vibration or oscillation should be transmitted to the optical switch, the vibration is decreased by the damping effects of the diaphragm and the space area, and hence is substantially not transmitted to the movable electrode plate.